Gemfile: Add the test group not to install rdoc in CI.

[junaruga]

This PR is not to install rdoc in CI, mentioned at #699 (comment) to avoid the issue #699.

You can check this page for Bundler group feature.

I wanted to do the following commands. However, the set -ex didn't work in Windows environment. So, I split the "depends" to "bundle config" and "bundle install".

- name: depends
  run:  |
    set -ex
    bundle config set --local without development
    bundle install

[rhenium]

ruby/stringio#71 seems to be the right solution for the CI error.

I agree it doesn't have to use the latest rdoc gem regardless. However, I think a better approach is to use bundle install --prefer-local.

Splitting groups (effectively removing rdoc from Gemfile) tells the CI to use the default gem version of rdoc. rdoc is still a default gem in Ruby master, but rdoc is one of the default gems that are planned to become bundled gems[*].

[*] https://bugs.ruby-lang.org/issues/19351

[rhenium]

I think a better approach is to use bundle install --prefer-local.

It didn't work. Apparently, this option makes it fetch from rubygems.org only when no versions of a requested gem is locally installed. Ruby 3.0 ships with test-unit 3.3.7 while we require test-unit 3.4.6 or later. bundle install --prefer-local can install rake-compiler because it's not installed at all, but fails to install a newer test-unit because a version of the gem is already installed. (related: rubygems/rubygems#6705)

[eregon]

rdoc is a dependency of RubyGems so I'm not quite sure it could become a bundled gem. From that issue it won't be until at least 3.4.
Although I suppose RubyGems could activate rdoc only when it needs it or so.
Removing rdoc from the Gemfile might be a good workaround, I'm not sure when ruby/stringio#71 will get merged and released (I hope soon but it does not depend on me).

I didn't know about --prefer-local. It'd be useful to have something like that which prefers default & bundled & already-installed gems to installing newer versions.

[junaruga]

..snip. Removing rdoc from the Gemfile might be a good workaround, ..snip..

I would like to keep the rdoc in the Gemfile for the cases with Fedora and the downstream Linux distro Rubies. I sent another PR #704 to pass the CI as a workaround.

[junaruga]

As the #699 was fixed, we don't need this PR any more.